diff --git a/docsite/latest/rst/playbooks2.rst b/docsite/latest/rst/playbooks2.rst index 47fb2f0d71..82120f8afd 100644 --- a/docsite/latest/rst/playbooks2.rst +++ b/docsite/latest/rst/playbooks2.rst @@ -857,30 +857,31 @@ Also see the module documentation section. Understanding Variable Precedence ````````````````````````````````` -You have already learned about inventory host and group variables, 'vars', and 'vars_files'. +You have already learned about inventory variables, 'vars', and 'vars_files'. In the +event the same variable name occurs in more than one place, what happens? There are really three tiers +of precedence, and within those tiers, some minor ordering rules that you probably won't even need to remember. +We'll explain them anyway though. -If a variable name is defined in more than one place with the same name, priority is as follows -to determine which place sets the value of the variable. Lower numbered items have the highest -priority. +Variables that are set during the execution of the play have highest priority. This includes registered +variables and facts, which are discovered pieces of information about remote hosts. -1. Any variables specified with --extra-vars (-e) on the ansible-playbook command line. +Descending in priority are variables defined in the playbook. 'vars_files' as defined in the playbook are next up, +followed by variables as passed to ansible-playbook via --extra-vars (-e), then variables defined in the 'vars' section. These +should all be taken to be basically the same thing -- good places to define constants about what the play does to all hosts +in the play. -2. Variables loaded from YAML files mentioned in 'vars_files' in a playbook. +Finally, inventory variables have the least priority. Variables about hosts override those about groups. +If a variable is defined in multiple groups and one group is a child of the other, the child group variable +will override the variable set in the parent. -3. facts, whether built in or custom, or variables assigned from the 'register' keyword. +This makes the 'group_vars/all' file the best place to define a default value you wish to override in another +group, or even in a playbook. For example, your organization might set a default ntp server in group_vars/all +and then override it based on a group based on a geographic region. However if you type 'ntpserver: asdf.example.com' +in a vars section of a playbook, you know from reading the playbook that THAT specific value is definitely the one +that is going to be used. You won't be fooled by some variable from inventory sneaking up on you. -4. variables passed to parameterized task include statements. - -5. 'vars' as defined in the playbook. - -6. Host variables from inventory. - -7. Group variables from inventory in inheritance order. This means if a group includes a sub-group, the variables - in the subgroup have higher precedence. - -Therefore, if you want to set a default value for something you wish to override somewhere else, the best -place to set such a default is in a group variable. The 'group_vars/all' file makes an excellent place to put global -variables that are true across your entire site, since everything has higher priority than these values. +So, in short, if you want something easy to remember: facts beat playbook definitions, and +playbook definitions beat inventory variables. Check Mode ("Dry Run") --check